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M. Sako, F. A. Harrison, R. E. Rutledge (Caltech)
We present uniform detailed spectral analyses of GRB X-ray afterglows to critically evaluate the statistical significances of the possible existence of X-ray emission lines. As shown by various authors, the observed spectra of several afterglows do show discrete features that appear to deviate from their respective best-fit continuum models. We perform Monte Carlo simulations to determine the true statistical significances of these features and find that, in all but possibly two cases, they are entirely consistent with statistical fluctuations typically observed in spectra with low number of counts. In most of the cases, where the presence for X-ray lines have been reported, the statistical significances are found to be extremely marginal (< 3\sigma), while two sources appear to exhibit features with slightly higher significance (\la 3.5\sigma). We discuss the implications of our results.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.